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Abstract While challenging, quantification of the near‐surface landfalling hurricane wind field is necessary for understanding hurricane intensity changes and damage potential. Using single‐ and dual‐Doppler Doppler on Wheels and in situ anemometer data, the wind structure of the very near‐surface boundary layer of Hurricane Laura (2020) is characterized. Small‐scale hurricane boundary layer (HBL) rolls (HBLRs) with a median size of approximately 400 m are present throughout much of the landfall, but are most vigorous in the eyewall. The maximum turbulent kinetic energy (TKE) and momentum flux associated with HBLRs occur in the eyewall and are much larger than previously documented at landfall. DOW‐derived and anemometer‐derived TKE values are comparable. Observed maximum surface gusts were consistent with the maximum radar wind speeds aloft, suggesting the importance of vertical transport within the HBL by sub‐kilometer scale structures for the enhancement of surface wind speeds. 

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Abstract The challenges associated with nowcasting quasi-linear convective system (QLCS) tornadoes are well documented. One key challenge is that QLCS tornadoes typically develop within mesovortices (MVs), but not all MVs are tornadic. This study used radar and in situ Pod data collected during the Propagation, Evolution, and Rotation in Linear Storms (PERiLS) field campaign to examine the characteristics that differentiate tornadic (TOR), wind-damaging (WD), and nondamaging (ND) MVs at various stages in their lifetimes and to investigate the low-level structure of QLCS MVs. Thirty-one QLCS MVs were manually identified and cataloged using the lowest elevation scans of the nearest WSR-88D and C-band on Wheels (COW) radars during the two years of PERiLS. TOR MVs, over their entire lifetimes, had stronger rotational velocities (Vrots), smaller diameters, and slightly longer lifetimes compared to WD and ND MVs. When MVs were analyzed during their pretornadic, predamaging, and prewarning phases (prephases), TOR and WD MVs had similar Vrots; however, TOR MVs typically had smaller diameters and contracted leading up to tornadogenesis, which could benefit nowcasters. In five cases, MVs were observed at the lowest WSR-88D elevation scans but were not visible in the COW data; the MV structure at different elevation angles for one case is presented. Eight Pods showed evidence of MV intercepts, demonstrated most notably by decreases in pressure. COW data, along with relatively weak wind speeds measured by Pods that collected data on MVs, suggest that vertical variations in low-level MV structure and strength can exist, which may not be adequately captured by the WSR-88D network. 

Abstract How do the atmosphere and airborne insects respond to the abrupt cessation and restoration of sunlight during a total eclipse? The Flexible Array of Radars and Mesonets (FARM), including three mobile Doppler on Wheels (DOW) radars, mobile mesonets, Pod weather stations, and an upper-air sounding system, was deployed as an unprecedentedly dense observing network in the path of totality of the 21 August 2017 eclipse that spanned the United States from its Pacific to Atlantic coasts. This was the first targeted dual-polarization radar, multiple-Doppler, and micronet study of the impacts of totality on meteorology and insect behavior. The study area was chosen to be completely sunny, nearly devoid of trees, with homogeneous, nonforested land use, and very flat. This resulted in as near an ideal observational environment as realistically attainable to observe the effects of a total solar eclipse absent the confounding effects of variable cloud shading, terrain, and land use. Rapid and substantial changes in the boundary layer and propagation of a prominent radar fine line associated with a posttotality wind shift mechanism different than previously hypothesized were observed. Profound and rapid changes in airborne insect behavior were documented, including descent and then reascent during the minutes immediately surrounding totality, with implications related to solar-related insect navigational mechanisms and behavior. 

Abstract This research attempts to use operational radar and satellite products to identify potential locations of quasi-linear convective system (QLCS) tornadogenesis, which can be difficult to predict. It is hypothesized that deep, discrete updrafts indicate portions of the QLCS capable of producing tornadoes, whereas shallower convection indicates more benign portions of the QLCS. To address this hypothesis, storm reports and storm surveys on 30–31 March 2022, during the second intensive observing period of the 2022 Propagation, Evolution, and Rotation in Linear Storms (PERiLS) field campaign, are used to identify locations of tornadoes within the QLCS. These tornado locations are then compared to representations of upper-tropospheric updrafts, namely, overshooting tops (OTs), which are identified with an algorithm using 1-min-resolution mesoscale sector data fromGOES-16Advanced Baseline Imager infrared brightness temperatures, and radar reflectivity cores aloft, identified with Multi-Radar Multi-Sensor (MRMS) 3D mosaic reflectivity products. Only a fraction (less than 30%) of tornadoes within the QLCS are associated with OTs, though over 85% of tornadoes are located near convective cores as indicated by cores of enhanced reflectivity at 9 km MSL. A numerical simulation of the event is also conducted using the Weather Research and Forecasting (WRF) Model which shows a strong relationship between simulated updraft intensity and reflectivity aloft. Given this apparent support of the hypothesis, the identification of updraft signatures within MRMS and high-resolution geostationary satellite data may ultimately help improve the identification of regions within QLCSs most likely to result in tornadoes. 

Abstract Cold pools play a range of important roles in quasi-linear convective systems (QLCSs), including maintenance via the development of new convective cells as well as baroclinic generation of horizontal vorticity. Although a number of QLCS cold pools have been characterized in the literature using one or a few sensors, their variability (both internally and across a range of environments) has still not been widely studied. This gap in knowledge extends particularly to high-shear low-CAPE (HSLC) convective environments common to the cool season in the southeastern United States, where the Propagation, Evolution, and Rotation in Linear Storms (PERiLS) field campaign was focused. PERiLS specifically targeted environmental and storm-scale processes in QLCSs, including their cold pools. Our analysis focuses on the heterogeneity and temporal variability of cold pools across short time and spatial scales using numerous surface and sounding observations across five PERiLS QLCSs. The PERiLS cold pools are generally weaker than those previously studied in warm-season, midlatitude QLCSs, likely due to the lower CAPE and higher relative humidity values common to HSLC environments during PERiLS. Nevertheless, the distributions of most PERiLS cold pool variables at least partially overlap with those of previously studied QLCSs. The median PERiLS measurement reveals a cold pool that is ≈2.5 km deep, having a surface temperature decrease of ≈−6°C, and a peak outflow wind gust of ≈13 m s⁻¹. In the spirit of a “cold pool audit,” we present the internal and case-to-case variability of these particularly well-observed QLCSs. Significance StatementEvaporatively cooled air masses (“cold pools”) are created by quasi-linear convective systems (“QLCSs,” also called “squall lines”), and they in turn play important roles in the maintenance and structures of QLCSs. There have been relatively few direct measurements of cold pool variability, especially for the frequently severe QLCSs occurring during the cool season in the southeastern United States. Numerous surface and upper-air measurements from the recent Propagation, Evolution, and Rotation in Linear Storms (“PERiLS”) field experiment are used to document Southeastern QLCS cold pools. The PERiLS cold pools were surprisingly similar to, albeit somewhat weaker than, those found in prior studies of warm-season QLCSs in other regions. 

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